1. Field of the Invention
This invention relates to an improved channel-selecting, presettable, rotary type tuning device, and more particularly, to a tuning device in which there is provided a tuning-position-determining unit having two or more tuning-position-determining elements whose positions may be adjustable. The tuning device of the present invention includes a slide member operably coupled to a variable tuning element and spring-loaded so as to abut the end of each tuning-position-determining element selected according to the rotation of the tuning-position-determining unit, means for rotating the tuning-position-determining unit so as to select tuning-position-determining element, means for moving back and forth each tuning-position-determining element thus selected; and means for temporarily releasing the slide member from its abutment on each tuning-position-determining element thus selected.
2. Description of the Prior Art
Prior art channel selecting, presettable, rotary type tuning device of the type described are of such an arrangement that when a channel-selecting member is rotated, a tuning-position determining element slidingly moves along a guide surface of a slide plate so that the next tuning-position-determining element may be brought into a desired position. Accordingly, undesirable forces tend to act on the slide plate to accumulate stresses on the slide plate and its guide portion. When a channel-selecting-tuning device is installed on a vehicle such as an automobile, the aforesaid stresses are released due to the vibration of the vehicle. As a result, a slight shifting of the slide plate relative to the tuning-position-determining element occurs thus resulting in inaccurate tuning to a frequency desired. For instance, the shifting or displacement of the slide plate by 1/100 mm results in a shifting of frequency by 1 KHz. When such a shifting in frequency exceeds 3 KHz, then the tuning device can no longer be serviceable in a satisfactory manner.
In addition, when the shifting of the aforesaid tuning-position-determining element occurs repeatedly the surface of the slide plate, which contacts the tuning-position-determining element, will wear and the position of the tuning-position-determining element will so vary that the variable-tuning-element can no longer be accurately positioned in.